Metal pipe of both corrugated and spiral rib design is widely used for drainage, culverts and other similar fluid conduits. Although susceptible to abrasion, steel pipe is preferred over concrete pipe and the like due to its comparatively high strength and low weight. These characteristics render metal pipe relatively inexpensive to manufacture, ship and handle while permitting its use in applications requiring it to support substantial soil overburden. Further, in recent years a particular spiral ribbed steel pipe has been introduced by W. E. Hall Co., of Newport Beach, Calif., the assignee of the subject application, that possesses hydraulic efficiency comparable to more costly concrete pipe as well as possesses superior structural capabilities for prolonged use in buried storm drain applications.
Since metal pipe is susceptible to corrosion, its use has heretofore been restricted primarily to culvert and storm drain applications. In sanitary applications, i.e. sewer systems, corrosion causing sulfuric acid is formed from hydrogen sulfide generated by waste products. Such waste products and/or acid renders the use of steel pipe in sanitary applications impractical since it rapidly deteriorates in the corrosive environment. As such, much heavier and more expensive concrete, lined concrete and/or vitreous clay pipe has traditionally been utilized for sanitary applications. Thus, although metal pipe is generally preferred because of its high strength and relatively low weight and cost, metal pipe has heretofore not been widely used in sanitary applications due to its susceptibility to corrosion.
In recognition of these deficiencies, prior art attempts to allow the use of concrete pipe as opposed to vitreous clay pipe for large size sewer applications while reducing the susceptibility to corrosion of concrete pipe have included: the installation of a thick corrosive-resistant plastic liner, and/or forming the inside of a concrete pipe with additional sacrificial concrete in the crown portion of the pipe.
Such prior art corrosion-resistant liners typically comprise plastic inserts sized to be received within each concrete pipe section. Such liners are commonly cast within each pipe section. Subsequently after the pipe sections have been laid in place, adjacent liners are bonded together with the intention of forming a seal to prevent corrosive fluids and gases from contacting the concrete pipe. Although such prior art concrete pipe/plastic liner solutions have proven generally suitable for large size sewer applications, the inherent high cost of such solutions has posed a severe impediment in construction products. Further the useful life of such prior art sacrificial concrete pipe solutions is finite, which requires widespread rehabilitation over time thereby mandating tremendous expense in down line rehabilitation costs.
In recognition of the general inability of metal pipe and concrete pipe for sewer applications, in recent years plastic pipe has been introduced into the marketplace. Although such plastic pipe withstands degradation caused by the corrosive environment found in sewer applications, its use has heretofore been primarily limited to small size sewer applications. In this regard, the structural integrity of plastic pipe is extremely limited such that in large size applications, the sidewall of such plastic pipe must be fabricated extremely thick or profiled to enable such plastic pipe to withstand compressive forces exerted in burial applications. Due to the high cost of such plastic material, the use of such plastic pipe in large scale sewer applications has been economically unfeasible. Therefore, in view of the specific factors encountered in large scale sanitary sewer applications, nearly all such applications have utilized costly concrete pipe having a sacrificial wall formed therein which significantly decay over prolonged use and thus will require costly rehabilitation and/or replacement over time.
In contrast to the waste product and/or acid environment encountered in sanitary applications, metal pipe utilized for burial storm drain applications additionally encounters substantial problems associated with its operational environment. In relation to burial storm drain applications, wherein metal pipe is the primary material candidate, long term exposure of the exterior of the metal pipe within the burial environment serves to corrode the exterior of the pipe while water and debris flowing through the interior of the metal pipe degrades the pipe through abrasion.
In an effort to prevent such corrosion effects, the interior of metal pipe has been lined with concrete in the hopes that a thicker lining would be more abrasion resistant and thereby resist deterioration and corrosion. However, there fails to exist any fail-safe means for anchoring concrete to the interior wall of metal pipe. Consequently, pieces of the concrete lining inevitably become detached from the pipe. When combined with the continual abrading action occurring therein, this quickly destroys the protective concrete layer. Additionally, concrete is susceptible to cracking and chipping as a result of mishandling, earth movement, and thermal stress. Such cracking and chipping results in corrosion of the steel surface in the vicinity of the chip or crack.
An alternative prior art approach to solving the corrosion and abrasion deficiencies of metal pipe for storm drain applications has been to fabricate the metal pipe from plastic laminated steel sheet material. One such prior art product is known as Black-Klad.TM., a product of Inland Steel Company of Chicago, Ill. Prior to rolling the steel sheet into a pipe section, one surface, i.e. that surface which forms the inner pipe surface, is laminated with a polymer material such as a polyethylene compound. The thickness of such lamination is limited to approximately 0.010 inch and is intended to resist degradation caused by corrosion and abrasion. However due to the comparatively thin thickness layer of plastic laminant, the laminant tends to wear through due to abrasion from sand, rocks, etc. and thereby expose the metal surface below. Further, during the pipe formation process, the thin laminant oftentimes is damaged due to metal cold roll forming procedures.
Attempts to apply thicker laminations to such prior art products have heretofore resulted in greater blistering and separation of the polymer compound from the metal pipe particularly when the pipe is exposed to flow applications. As such, the application of a protective polymer layer to metal pipe has heretofore been rendered ineffective.
Therefore because the prior art interior lining of metal pipes have proven susceptible to abrasion and corrosion, and since abrasion resistant inert linings such as those constructed of concrete or an inert polymer material have failed to remain effectively anchored to the metal pipe walls, metal pipe has heretofore been unacceptable for use in sanitary applications such as sewer drains.
As such, there exists a substantial need in the art for a sufficiently thick coating or lining which may be securely applied to metal surfaces to maintain the integrity thereof when the metal pipe is placed in a corrosive environment and to remain thereon without blistering during the pipe formation process. Further, there exists a substantial need in the art for an improved metal pipe with an inert protective lining constructed of a polymer material such as polyethylene which would resist the attack of sulfuric acid as well as resist other forms of corrosion encountered in sewer application.